1. Field of the Invention
The present invention relates to a method of manufacturing a cylinderical billet and more particularly to a method of manufacturing a cylindrical billet having a predetermined length usable as starting material for producing a pipe.
2. Description of the Prior Art
To practice the conventional method of manufacturing a seamless steel pipe Mannesmann type plug mill, Mannesmann type assel mill or the like have been heretofore employed. In the conventional manufacturing facilities as mentioned above seamless steel pipes are typically produced by way of the steps of heating a solid billet having a round or square cross-sectional configuration, piercing it to form a cylindrical billet which is usable as starting material for making a required steel pipe and causing it to be subjected to diameter enlarging or thickness reduction rolling.
In order to assure that seamless steel pipes having a high quality are manufactured at a reduced cost a variety of technical research and development have long since been conducted with respect to each of the above-mentioned manufacturing steps. In practice, however, any remarkable improvement fails to be achieved in respect of saving of material and thermal energy, increased efficiency of operation and reduction of manufacturing cost.